Pineal gland

The pineal gland is a small, pine-cone shaped structure considered to be part of the epithalamus. It is unpaired and situated in the midline. 

Gross anatomy

The pineal gland typically measures 7 x 6 x 3 mm in size and is situated in a groove between the laterally placed thalamic bodies ^1-6. Appearing to arise from the gland are two laminae. Above is the habenular commissure and below it is the posterior commissure. 

Relations

• anteriorly - : third ventricle (pineal recess)
• posterioinferiorly - posteroinferiorly: superior cerebellar cistern
• superiorly -: internal cerebral veins, vein of Galen (posteriorly), stria medularis, splenium of the corpus callosum and velum interpositum
• inferiorly -: superior colliculi of the midbrain

Blood supply

The pineal gland receives its blood supply from fine branches off the posterior choroidal arteries and drains superiorly by multiple branches eventually into the great cerebral vein of Galen ³. 

Embryology

The pineal gland arises during the seventh week of gestation from a thickening of the ependyma at the posterior most aspect of the third ventricle ⁵. 

Physiology

The pineal gland produces melatonin which affects the modulation of wake/sleep patterns and photoperiodic (seasonal) functions. It is also thought to have a reproductive function and has been associated with the onset of puberty ⁷. Unlike much of the rest of the brain, it is not isolated from the body by the blood-brain barrier.

Radiographic features

Plain films

The pineal gland has a predilection for calcification which is invariably histologically present in adults but rarely seen below the age of 10 years ⁶. Calcification is visible on lateral skull x-rays in 50-70% of adults ⁶. The habenular commissure also calcifies and is visible as a small C-shaped (open part posteriorly) density above and infrontin front of the pineal calcification. 

CT

With CT'sCTs far higher contrast resolution calcification is almost always visible in the adult pineal gland, sometimes visible as specs embedded in a small soft tissue nodule similar in density to grey matter. In children under the age of 5 years no calcification is present, but prevalence increases rapidly with age, reaching a plateau at about 30 years of age ⁵. 

MRI

MRI is the modality of choice for evaluating the pineal region although its sensitivity to calcification on conventional sequences is poor (note: susceptibility weighted imaging (SWI) has sensitivity to calcification similar to CT). 

The gland appears as a small nodule of tissue with similar intensity to grey matter. It enhances vividly during contrast administration as it is outside the blood brain barrier.